The first season could be doing bad (financially of course) and they realize that there won't be budget for a second thus they just wrap it up with the first season.

Either way, if they never make a sequel it's usually because the first didn't make enough money (usually in Japan, USA licensing tends to be pocket change in the anime market, unless it's DBZ, Pokemon, and such).

Not enough money, nobody watches it in Japan, no one supports it, not enough money, other projects are going on, they went too fast and aren't ready to continue it right away, etc... I don't really know anything.

Sad that the Berserker anime didn't get enough rating to continue. Then again, the mangaka is SUPER slow in releasing chapters, so I guess it doesn't really matter.

In September 2010, a wraparound jacket band on volume 35 of the Berserk manga announced a new anime project. The project was later revealed to be a series of films intended to adapt the entire manga, starting with three films adapting the "Golden Age" story arc.